This invention relates to cables and methods for inserting cables into conduits. More particularly, this invention relates to fiber optic cables and the like, as well as assemblies for facilitating insertion of the cables into semi-rigid conduits, such as PVC pipes. A method for inserting the cable assembly into a conduit is also disclosed.
Heretofore, communications-cables, coaxial cables, fiber optic cables and the like, have been inserted into extended sections of pipe or conduit using a variety of different methods. The xe2x80x9cpullxe2x80x9d method generally involves attaching a pull cord or pull tape, which is already disposed within the conduit, to one end of the cable, and then pulling the cord or tape from the other end of the conduit until the cable extends through the length thereof. This method has several disadvantages.
First, the amount of force applied to the cable in order to pull the cable through the conduit must remain relatively low. Generally, fiber optic cables will not withstand forces beyond about 600 pounds of force before the optical properties of the glass fibers are significantly affected in a negative manner. Secondly, the force that will be exerted on the cable itself forces the cable manufacturers to use several layers of strength members within the cable itself. These strength members are typically tightly woven sheaths made from fibers of steel or Kevlar(copyright), or some other aramid fiber that exhibits little or no elongation. The strength members are formed and fixed as inner layers of the cable, usually beneath an extruded outer sheath of high-density polyethylene. Because the glass fibers are not elastic, and will be damaged easily due to microbending and other mechanical strains, the strength member must bear most of the force imparted by the pulling and other handling mechanisms in order to protect the optical fibers. These extra layers of strength members add a significant amount of cost to the fiber optic cables.
Another commonly used method for inserting cables into conduits is the xe2x80x9cpushxe2x80x9d or xe2x80x9cblowxe2x80x9d method, where the cable is subjected to high pressure air, which blows the cable assembly through the conduit. Of course, the cable assembly may also be sucked through the conduit by virtue of a vacuum or low pressure applied to the conduit at the remote end. This method also has limitations, and requires substantial energy and air pressure to force the cable assembly through long lengths of conduit.
Further, a disadvantage of both methods relates to friction between the outer sheathing of the cable and the inner wall of the conduit. The outer sheathing of a fiber optic or coaxial cable is typically made of an extruded polymer, such as polyethylene or polyvinylchloride, generally having a melting point or softening point in the range of 100 to 150xc2x0 C. The friction generated between the cable sheathing and the inner wall of the conduit substantially limits the speed with which the cable may be drawn through the conduit. If the cable is drawn through the conduit at an excessive rate of speed, certain contact areas of the cable sheathing will melt or burn through. To combat this problem, massive amounts of lubricants have been used in conjunction with the cables and conduits. Supplying the amount of lubricant necessary to pull the cable through an extended length, even at a moderate rate, is an expensive and time-consuming process. Moreover, these lubricants can negatively affect the environment around the cable.
Therefore, it would be advantageous and desirable to provide a cable assembly that reduced friction between the cable and the inner wall of the conduit, which either substantially reduces or eliminates the necessity of using lubricants, and which increases the speed with which the cable could be inserted into the conduit, while providing a minimal amount of stress on the optical fibers to allow for safe installation. Moreover, it would be desirable to provide a cable assembly and method that would allow a substantially greater force to be applied the cable assembly for insertion into the conduit. Further, it would be desirable to provide a cable assembly that could be inserted more quickly and less expensively than those provided heretofore.
Accordingly, it is an important object of the present invention to provide a cable assembly having an outer jacket disposed about a cable, so that the cable is in slidable relation thereto.
It is another important object of the present invention to provide a cable assembly that may withstand a substantially higher pulling force than that achieved heretofore, without endangering the critical portions of the cable, such as copper, optical fibers, etc.
Yet another important object of the present invention is to provide a cable assembly and method that allows a cable to be inserted into a conduit at a much higher speed and longer pulling distance than has been achieved heretofore, without the necessity of increasing the level of strength of the cable itself.
Still another important object of the present invention is to provide an apparatus and method that allows several cables to be efficiently inserted into a conduit at high speed using a single outer jacket.
It is yet another important object of the present invention to provide a less expensive and more efficient alternative to the current methods and devices used to insert cable into a conduit.
Another important object of the present invention is to provide a cable assembly having an outer jacket that provides abrasion resistance and has a high enough melting point to prevent any burn through due to the friction caused between the outer jacket and the inner wall of the conduit.